A conventional electromagnetic clutch with an elastic member for easing the impact force transmitted to the drive shaft of a compressor is disclosed in U.S. Pat. No. 3,774,739 to Higuchi, and is illustrated in FIG. 1. The clutch comprises pulley 1 which is supported on bearing 2 and is rotated by an automotive engine through a belt (not shown). Pulley 1 is formed of a magnetic material in which one or more concentric arcuate or annular slits 3 are formed to define a plurality of concentric annular magnetic poles. Hub 5 is fixed on the terminal end of drive shaft 4. Holder plate 8 and the outer end portion of hub 5 are formed with concentrically disposed cylindrically shaped flanges 81 and 51. Rubber member 9 is disposed in the space defined between axial flanges 81 and 51. Therefore, armature plate 6 is connected to hub 5 through holder plate 8 and rubber member 9. Rubber member 9 therefore functions to ease the transmission of sudden torque changes to the drive shaft. These sudden torque changes impart an impact force on rubber member 9 which induces a bending or shearing stress on the rubber member. This intermittently applied stress to the rubber member may cause the rubber member to crack and eventually be destroyed.
One solution to overcome the above mentioned disadvantages is disclosed in U.S. Pat. No. 4,624,354 to Koitabashi and is illustrated in FIG. 2. This electromagnetic clutch comprises holder plate 8' and outer end hub 5' both of which are provided with concentrically positioned polygonally shaped axial flanges 81' and 51', and rubber member 9' which is disposed between axial flanges 81' and 51'. The polygonal shape reduces the shearing stress in the rubber member and the durability of the rubber member is thus improved.
However, the rubber member used in both of these conventional electromagnetic clutches is affixed on the axial flanges 81' and 51' by adhesive materials, and the adhesive strength of the adhesive materials fails with the passing of time. As a result, the rubber member becomes detached from the surface of axial flanges 81' and 51'. Also, the adhesive portion of the rubber member may be damaged.